From time to time we see people with little formal education in physics, esp. plasma or particle physics, proposing something that seems easy but is actually very difficult or impractical

(Common issues include that magnetic lenses and magnetic containment is generally difficult, that bending or decellerating particles tends to lose energy by cyclotron radiation or bremstrahlung, that it is difficult to have a high density of charged particles in any given space, etc.)

Is there a chance we could have a quick primer on the factors that sink many of these proposals?

I am no plasma physicist but relative to fusors, you provided part of the answers yourself; however, the bottom-line is density/charge effects and the fact fusors do not use brute force methods but depend on a rare quantum mechanical effect for their performance - that is, a fusor requires a high density plasma (compared to tokamak's) and simply depend on random collisions that can, through very rarely, allow "tunneling" through the Coulomb barrier (and this is a purely quantum mechanical effect and its exact calculation is not easy.)

Hence, these extraordinarily rare reactions create extremely little energy production at a large cost in energy input to create the required plasma. Increasing the plasma temperature or further increasing the density does little to increase the rate of fusion via this rare tunneling process. That limits these fusor based devices and why they simply do not really 'scale' up. Also, why these devices deliver such incredibly tiny fusion yields compared to the staggeringly large number of deuterium ions needed (which do nothing except soak up energy that is converted to wall heat.)

However, calculation of collisions with charge effects and a "fixed"capture radius is not terribly difficult and is accessible to a junior level physics student - some past posters have partly and seriously addressed this and their calculations are available to anyone who wants to search the forum.

Yet, any such information would be mostly a waste: the vast majority of these people neither are interested in or would care what the math/physics say's, or even the 'why' (if they did, they can easily find that information both here and on line at other sites.) Rather, they will feel that they alone have had the brilliant insight to solve this problem and we poor fools here need to be enlighten by their sheer genius.

Many of their ideas could be built (if rather involved) but these singular posters have some issues: 1) They have less than zero interest in building anything 2) No idea that they come up with has ever or can address the fundamental limitation of any fusor - the dependence on tunneling - a rare quantum phenomena 3) Finally, they are just too often convinced that they alone are correct and all of us here, or physicist and people in general, just fail to understand their brilliance so why bother with reading dry facts that miss their insight to solving the problem?

That all said, it is an interesting subject and if you want, maybe that would be a good series of posts for you to do: read the past posts here, digest them along with information from books/on-line and write up a detailed analysis of why fusors can never be scaled up to produce power.

Dennis said virtually everything I would say. The FAQs are for "doers" who need hard information that has been condensed and served up on a basis of continuing need for what are hoped to be real doers arriving here. We have a series of FAQs on theory which seem to be rarely read by the folks who are pretty much "armchair fusioneers" with overactive imaginations and half-baked ideas that they wish others would try out for them. They want to supply the great ideas so that others may toil and use up their treasure to implement.

The best among us recognize these types and tend to give them little recognition.

We could create a FAQ outlining worthless ideas and concepts based on good physics, but they would not care and perhaps not bother to read such a FAQ as the vast majority of newbies seem to do until such a suggestion is made to them.

Again, for some reason I seem to do all the FAQs. Anyone can do a FAQ so long as it is needed, well done and presented in a useful, flowing format. All FAQs should be accurate and not misleading. I have, on several occasions, been called on errors within my FAQs in subsequent replies. I have corrected the original, giving credit within it for correction to the person finding my faux pas. Thus, in spite of what I felt was my best effort, I made a mistake, admitted it and corrected it. I worry others here are afraid to do a FAQ for fear of getting something wrong.

If you feel a need is there, do a FAQ yourself. Pick up your courage, belly up to the bar and expound to us.

Richard Hull

Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

(I feel this is maybe needlessly harsh. A lot of ideas seem like they would be simple and practical to somebody who has learned "enough to be dangerous" about how magnetic fields control particles, for example.)

Fusors are notable because they are extremely simple. A working fusor can be designed and built with very little mathematical study of its operation. It is well understood that fusors are very inefficient, but they are easy to get working somewhat. The other common form of simple-to-design fusion reactor is the Beam-On-Target accelerator machine used in many commercial neutron generator fusion systems and also by Rapp Instruments.

From time to time, people have ideas for more complicated fusion systems. Unfortunately these are often doomed to failure. People who know a fair amount of particle physics often don't realize just how damaging some of the losses and limitations inherent to plasma systems are, or how additional complexity can be counter-productive, especially without detailed modelling.

- Losses, losses, everywhere: There are a very large number of ways that your hard-earned energy can leak out of a system, and usually making things more complicated adds more ways. For power generation projects trying to reach break-even, this steals the lifeblood of the system. For projects that are just trying to improve on fusors or BOT, losses can easily make an improvement in efficiency into a loss.

- Brehmstralung, Cyclotron, and Synchnotron Radiation: High energy charged particles do not like being decelerated or made to move in curved paths. Trying to do either can make them bleed energy in the form of X-rays. This means that any use of magnetic lenses to bend or focus plasma, or any use of electrostatics to decelerate particles may create a very large loss (and an extra source of radiation).

- Brillouin Limit and Space Charge: Because of repulsion between like charges, there is a sharp limit on how dense one can make a plasma (with a given strength of magnetic and other containment forces). And many plasmas will not be neutral, exacerbating the problem. Making magnetic containment or focusing fields more powerful tends to run into the previous problem with cyclotron radiation losses.

- Self-defocusing beams: Repulsion in a non-neutral particle beam will make it spread out. Beams passing through each other or a cloud of gas or plasma will also spread out. Both of these lead to problems with systems that try to use a beam of particles more than once.

It is worth noting that many of these issues are also problems for ion thrusters in space and for some types of energy weapons, as well as making the Bussard Ramjet a scheme of questionable practicality.

I have made a few corrections in spelling and structure to offer. I have put my suggested amendments below in what I think is a bit more free flowing.

begin......

Fusors are notable because they are extremely simple. A working fusor can be designed and built with very little mathematical study of its operation. It is well understood that fusors are very inefficient, but they are relatively easy to get working. The other common form of simple-to-design fusion reactor is the Beam-On-Target, (BOT), accelerator machine used in many commercial neutron generator fusion systems and also by Rapp Instruments.

From time to time, people have ideas for more complicated fusion systems. Unfortunately, these are often doomed to failure. People who do not know a fair amount of particle physics often don't realize just how damaging some of the losses and limitations inherent to plasma systems are, or how additional complexity can be counter-productive, especially without detailed modeling.

- Losses, losses, everywhere: There are a very large number of ways that your hard-earned energy can leak out of a system. Often, making things more complicated adds more ways for such leaks to occur. For power generation projects, trying to reach break-even, this steals the lifeblood of the system. For projects that are just trying to improve on the output of fusors or BOT, so called improvement ideas can actually turn what was hoped to be an improvement in efficiency into a net loss.

- Brehmstralung, Cyclotron, and Synchnotron Radiation: High energy charged particles do not like being decelerated or made to move in curved paths. Trying to do either can make them bleed energy in the form of X-rays. This means that any use of magnetic lenses to bend or focus plasma, or any use of electrostatics to decelerate particles may create a very large loss (and an extra source of radiation).

- Brillouin Limit and Space Charge: Because of repulsion between like charges, there is a sharp limit on how dense one can make a plasma, (with a given strength of magnetic and other containment forces). Many plasmas will not be neutral, exacerbating the problem. Making magnetic containment or focusing fields more powerful tends to run into the previous problem with cyclotron radiation losses.

- Self-defocusing beams: Repulsion in a non-neutral particle beam will make it spread out. Beams passing through each other or a cloud of gas or plasma will also spread out. Both of these lead to problems with systems that try to use a beam of particles more than once.

It is worth noting that many of these issues are also problems for ion thrusters in space and for some types of energy weapons, as well as making the Bussard Ramjet a scheme of questionable practicality.

end.......................

Ian, I suggest you proudly publish your work in a FAQ under your name.

In the end, I was not too harsh...........I forced you to belly up to the bar and you rolled up your sleeves and did good.

I had teachers like I am now when in college. I learned from them. A little tough love can make someone try just a bit harder, provided they have the right stuff.

If I were a teacher, I would beat up on my students. If they wanted to learn, I would teach them. The naturally gifted, self-assured and strong would slide through, quite naturally, with A++ grades, remembering me as a bastard of a teacher. Those who were ultimately capable would pass not because of me, but in sheer spite of me. Maybe, one day, The best of these might remember I helped give them a bit of courage and spine in the face of adversity and uncertainty. All the rest would rightfully rise or sink where they will in life and society.

The people at the top and bottom of my class would both remember me as a bastard. It is those that I really helped, by whatever methodology, are those that I value the most. "They had guts...And guts is enough"

All people at the bottom can, ultimately, point their fingers to a vast, life-long, list of reasons they are on the bottom and why they can't get up off the floor.

Pass on the naturally gifted and strong. Push and forcibly herd the weak and insecure if there is hope seen in them. Let all others go their way.

Thanks, Ian, for your service to fusor.net. You did good.

Richard Hull

Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Have you tried? Give it a shot. If you cannot post to them, then if you approve of my small improvements, I will post it in your name.

Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.